Not able to get auth-access-token from facebook using authorisation code

I want to create a Facebook enabled login for my ember app, In frontend i am using torii to get the authorisation code from facebook and then i'm posting it to rails enabled backend to get access-token(In the backend i am using omniauth-facebook+devisetokenauth).

But when i do post call from frontend to backend (localhost:3000/user/:provider ) i get following error

`Started GET "/omniauth/facebook?code=AQBy6c48CohDlPqI-fmfQeE9LN6NFFdtBZDuziflFkPjrFKACeT9OwHtfbIpUDufQbX3gXcArcJJRtPv9R9kXtHFWMDZ16k2r3Q6jJ0BdaNqkwwxwjUYmKUhZyllsDYP_GkS5KSq9brqvaSnjJqTI-KZR2s3AbNzYdbyy-Gdzh9zVhpeWTsD0yPBysjdgq2HU9Kj6dCwH37yNp2DnDfMHPWeCev2qjw_N8GU1R-3HOco9dV-MWNVNiQeKP8u88nioPmEL35FlSpycIy43lBL-hgN-iGFnHoVuxjWbH0Nhos_1QiZAbhYLlSjPE_RKu4sX-HT4ldQdsGMh6RoFCKoNTL0&provider=facebook&resource_class=User" for 127.0.0.1 at 2018-02-19 13:57:22 +0530 I, [2018-02-19T13:57:22.043998 #28320] INFO -- omniauth: (facebook) Request phase initiated.

ArgumentError (key must be 32 bytes): ` And is this the right approach.

Thanks